To supress effectively vibration of a car body while maintaining a comfortable riding on a vehicle.

The vertical absolute velocity x' of a body 11 is detected, and the vertical relative velocity y' relative to a lower arm 13 of the car body 11 is detected. Then, when the directions of the velocities x' and y' are not coincident with each other, the target damping factor C* is determined to be a small value, and when they are coincident with each other, the target damping factor C* is determined to be a large value as the velocity ratio x'/y' becomes large. The amplitude X of the vertical vibration of the car body is detected to limit the target damping factor C* to a small value when the amplitude X is small. Thus, a sudden increase of the damping factor is avoided at the start of vibration of the car body 11, and a comfortable riding is maintained. And, in a state in which vibration of the car body 11 becomes big, since the threshold value of the damping factor is also set to be a large value, a sufficient damping force is obtained against vibration of the car body 11 to supress effectively vibration of the car body 11.